The standard picture of cosmology assumes that a phase transition
(associated with chiral symmetry breaking after the electroweak
transition) occurred at approximately
seconds after the Big Bang to convert a plasma of free quarks
and gluons into hadrons. Although this transition can be of
significant cosmological importance, it is not known with
certainty whether it is of first order or higher, and what the
astrophysical consequences might be on the subsequent state of
the Universe. For example, the transition may give rise to
significant baryon number inhomogeneities which can influence the
outcome of primordial nucleosynthesis as evidenced in the
distribution and averaged light element abundances. The QCD
transition and baryon inhomogeneities may also play a significant
and potentially observable role in the generation of primordial
magnetic fields.

Rezolla et al. [47] considered a first order phase transition and the nucleation of
hadronic bubbles in a supercooled quark-gluon plasma, solving the
relativistic Lagrangian equations for disconnected and
evaporating quark regions during the final stages of the phase
transition. They numerically investigated a single isolated quark
drop with an initial radius large enough so that surface effects
can be neglected. The droplet evolves as a self-similar solution
until it evaporates to a sufficiently small radius that surface
effects break the similarity solution and increase the
evaporation rate. Their simulations indicate that, in neglecting
long-range energy and momentum transfer (by electromagnetically
interacting particles) and assuming that the baryon number is
transported with the hydrodynamical flux), the baryon number
concentration is similar to what is predicted by chemical
equilibrium calculations.

Kurki-Suonio and Laine [37] studied the growth of bubbles and the decay of droplets using a
spherically symmetric code that accounts for a phenomenological
model of the microscopic entropy generated at the phase
transition surface. Incorporating the small scale effects of the
finite wall width and surface tension, but neglecting entropy and
baryon flow through the droplet wall, they demonstrate the
dynamics of nucleated bubble growth and quark droplet decay. They
also find that evaporating droplets do not leave behind a global
rarefaction wave to dissipate any previously generated baryon
number inhomogeneity.